The Menstrual Cycle: Nutrition, Training & Fat Loss

The menstrual cycle has a huge impact on any woman trying to get in shape.

Scientific research on women has helped us understand much more about how your cycle affects your ability to lose fat, improve performance and optimise body composition than ever before. 

The problem is that so many women still don’t fully understand how their cycle can be holding back their results in the gym.

This article is a comprehensive analysis of everything you need to know about menstrual cycles and exercise – from fat loss training principles and programming, to diet, lifestyle and mood. Here’s what you’ll learn.

• Can you train throughout your menstrual cycle?
• Is it harder to lose fat while on your period?
• Does dieting affect your period?
• Should you be worried if menstruation stops?
• Is there a way to change your diet or training sessions to optimise fat loss?

INTRODUCTION

Many women fear the onset of their cycle. It comes with discomfort, irritability, cramps, and cravings. If you’re a serious gym goer, that can make your workouts much tougher to get through.

The constant fluctuations in hormone levels mean that everything from your energy levels and strength, to your appetite and mood, can change from one day to the next. 

And whilst a regular cycle is a sign that you are healthy, many women choose to skip the gym because of these symptoms.

But should you skip the gym when you’re on your period?

Definitely not.

But being aware of how your cycle affects your endurance, strength and ability to tolerate exercise training, allows you to take advantage of the many biological ‘windows of opportunity’ that are presented to you along the route of your monthly cycle.

Knowing how to adapt your workouts and diet can play an important role in fat loss, athletic performance and muscle build. 

Your menstrual cycle isn’t an excuse to skip sessions; it’s simply an opportunity to switch your approach and optimise your body composition through training knowledge.

Here’s everything you need to know…

MENSTRUAL CYCLE BASICS

The most obvious place to start is to look at exactly what happens over the course of a typical cycle. And I say that through gritted teeth, because I know from experience that a ‘normal’ cycle for one woman is much different to another.

Every woman is different

Whilst some women might have a steady month-to-month cycle, many women experience phase-to-phase variations where cycles last anywhere from 21 days to 35. 

And some women of course either have stopped their periods (menopause) or suffer irregular periods because of hormonal disturbances or medications.

However, when you look at the collective data, the average monthly cycle is 28-day long, so for the purpose of this section that’s the context we’ll use.

Menstrual cycle phases – how hormones shift week by week

Although there’s a lot of changes to hormones over the month, we’ll focus here on the ones that affect training and nutrition the most – namely 

• Estrogen
• Progesterone
• Testosterone 
• Luteinizing Hormone

Although there’s a fair bit of biology involved here, it’s important to understand this going forward so that you can best manipulate training and nutrition to suit your body.

The hypothalamic-pituitary connection

Before we get into the bulk of menstrual science, it’s worth giving props to two things in particular – the hypothalamus and the pituitary gland. Together they regulate hormonal release over the course of a cycle.

They act as the computer hard drive that pings messages to the ovaries to control the release and pacing of each individual hormone – much like a conductor does with an orchestra.

Presuming that your cycle is normal, there are three main phases that occur over the 28-day cycle period. A cycle is counted from the first day of one period to the first day of the next period. Here’s what you can expect.

1. The follicular phase – Days 0-14

Because each phase rolls on from the one preceding it (they occur as a perpetual cycle), there’s no real start or end point. However, it makes sense to look at the follicular phase first as it is when menstrual bleeding begins so gives us a big landmark at which to count the days.

Bleeding occurs because the egg that was released during the previous cycle was unfertilized and the lining of the uterus started to break down. Bleeding may occur for anything from 2-5 days.

During the follicular phase, the hypothalamic-pituitary axis signals an increase in follicle stimulating hormone (FSH). It does this to order the follicles of the ovaries to develop a mature egg in preparation of fertilization. At the same time, there is a steady increase in estrogen from the ovaries – initially quite slowly, but much more steeply towards day 12 or so. It does this to help the lining of the uterus grow and thicken in anticipation of ovulation.

When estrogen gets to a certain level, it triggers a sharp surge in another hypothalamic-pituitary hormone called luteinizing hormone (LH). This sudden increase works like a pin – it bursts the mature follicle, and in doing so it releases an egg for fertilization.

2. Ovulation – Day 14

Roughly between days 13 and 16, ovulation occurs. During this short phase, the egg is ushered towards the fallopian tube because of an increase in blood flow and connective tissue contraction.

At this point, there is a small peak in estrogen and another hormone, progesterone, begins to increase too. It is released from the corpus luteum which is a temporary endocrine gland. Together, estrogen and progesterone work to keep the lining of the uterus thick and healthy to maximise the chances of fertilisation.

During the ovulatory phase, you’ll also find a small peak in testosterone. Many believe that this is to boost libido at the time when the potential for fertilization of the egg is optimised. It is also an important regulator of exercise quality, which we’ll find out later on.

3. The luteal phase – Days 15-28

This phase – otherwise referred to as premenstrual phase – is the gap between ovulation and bleeding. Presuming that the egg hasn’t been fertilised, the combined high levels of estrogen and progesterone sends a message back to the hypothalamic-pituitary axis telling it to ease off (what’s called a negative feedback loop). This, in turn, means that no additional follicles mature and ovulate and the corpus luteum stops producing progesterone causing the lining of the uterus to ultimately degenerate. This results in bleeding.

THE IMPACT OF MENSTRUAL CYCLES ON PERFORMANCE

Taking into account how your body adapts and changes over the course of your cycle allows you to plan workouts more appropriately.

According to one research paper, “Women’s weight and body composition is significantly influenced by the female sex-steroid hormones. Levels of these hormones fluctuate in a defined manner throughout the menstrual cycle and interact to modulate energy homeostasis” [1].

For that reason, here’s all you need to know about how your cycle can affect the way you train.

Changes in Body Temperature, Time to Exhaustion and Fatigue

The monthly menstrual cycle isn’t just associated with rhythmic changes in hormone levels; it is also accompanied by changes in autonomic thermoregulation – fluctuations in core body temperature [2].

Again, although this might differ from woman to woman, the typical pattern of temperature changes seem to be similar across the 28 days.

Post-ovulatory increase in body temperature

Basal body temperature (BBT) is a common method of measuring core body temperature fluctuations. Your BBT is your lowest body temperature, and is often found during sleep and is often measured upon waking. It gives us a fairly reliable idea of what happens to thermoregulation across the 28 days.

Firstly, there doesn’t appear to be any change in body temperature during the early or late follicular phases. This means that the body is regulated at a normal 36-37 degree Celsius. Couple this with the increase in estrogen, and chances are you’ll feel full of energy and your mood will be positive too.

However, shortly after ovulation when progesterone is on the increase, there is a gradual elevation in body temperature. It is more evident in the morning but will facilitate itself throughout the luteal phase [3]. This can lead to poor thermoregulation and feelings of excessive heat, particularly when exercising.

You might feel more fatigued than normal

The rise in temperature during the luteal phase may mean you feel warmer during your workouts, or run the risk of acute dehydration through perspiring. 

Current consensus suggests that there may also be a decrease in time to exhaustion too – you’ll tire much quicker than during the follicular phase. This more than likely due to an increase in general cardiac strain [4].

However, small pockets of research contradict this and show that some women can adapt to luteal-phase changes in temperature through reduced urination and increased sweating [3]. Like anything, it is important to monitor how you feel during your workouts and adapt according to individual tolerance.

Pain tolerance

Women are built with stamina in mind, and for that reason you have a muscle fibre distribution that favours endurance (much higher proportion of type I fibres and less type II). 

The consequence of this is that whilst you might not necessarily have the absolute strength of your male counterparts, you can tolerate much higher submaximal volume… and can recover much more efficiently between sets too.

Women are machine-like in their ability to tolerate pain – especially during the follicular phase. This can lead to favourable increases in strength and tolerance at high intensities. Ramping up total session volume and decreasing rest periods is a good way forward.

Exercise performance

The majority of data currently suggests that there is no change in maximal oxygen uptake, heart and ventilation rate or blood volume at various time points across the menstrual cycle. There is, however, a big difference in perceived exercise stress. If you were to do the exact same workout over the two phases, it would feel much harder in the luteal phase.

HOW DO YOU OPTIMISE PERFORMANCE FOR FAT LOSS

Ramp up the intensity during the follicular phase.

The follicular phase has so far pointed to an increase in pain tolerance, normal body thermoregulation, and limited potential fatigue. 

The force-generating characteristics of your muscle fibres are at their highest too.

But with all of those positives comes the negative… you might find that your metabolic rate is slower here than in the post-ovulatory period. Some studies showing that your resting energy expenditure can be at its lowest around one week before ovulation [5] meaning a dip during the follicular phase.

During the late follicular phase, testosterone and estrogen are both relatively high, whilst progesterone is still quite low. 

Testosterone, as we know, is an anabolic hormone that promotes strength. 

Estrogen itself also has anti-catabolic properties that reduce muscle damage and promote recovery. Progesterone though is a catabolic hormone that can counteract the effects of both testosterone and estrogen.

This means you’re in a great place to really push yourself and hit the gym for some high-intensity strength and cardio work. The estrogen to progesterone ratio is in your favour to make some big gains and you’ll feel strong.

Research also suggests that weight training in the follicular phase results in higher increases in muscle growth than in the luteal phase too [6]. 

This is more than likely due to higher circulating anabolic hormone levels. And with the high capacity for adaptation, you’ll soon be rewarded for your hard work with some big gains.

Racking up a high calorie burn with some higher volume-load and more frequent strength training will really help you to boost your lean mass and change your body composition.

Focus on endurance during the luteal phase

As ovulation passes and you move into the luteal phase you’ll notice that your metabolic rate begins to pick up again. 

Your force capacity and strength will likely begin to taper off, although there are one or two studies to suggest that it may remain high throughout the early luteal phase too.

In this phase, progesterone levels peak, meaning your response to strength training won’t be as high. 

But what you lose in strength, you gain in endurance – and your metabolic rate will be ticking over slightly higher than in the previous two weeks. 

Unfortunately, your basal body temperature begins to increase and pain tolerance isn’t as high, so don’t expect to be setting any PRs on the big lifts.

You don’t have to stop strength training (and you shouldn’t), but just be aware that you might not feel as strong and your perception of how hard your sessions are will go up. 

A good plan here would be to take the foot off the gas a little and introduce more lower-intensity weight training coupled with moderate-intensity cardio or circuit sessions. Deload sessions and endurance sessions with an emphasis on duration and not intensity also work well here.

THE IMPACT OF MENSTRUAL CYCLES ON DIETING AND NUTRITION 

Should you diet on your period?

The simple answer is, yes. It’s dogmatic to think that you can’t ‘diet’ when you are on your period. 

Of course, the word diet means different things to different people, so we need to look at exactly what you need to do with your food intake to maximise fat loss.

Think about it logically – if you take time away from your diet plan each month, your progress will be much slower. 

To some extent you’d be starting again each time you went back on a calorie deficit. 

You’ll not train as well either if you aren’t getting a sensible balance of nutrients (more on that later).

What you should focus on though is optimising the way you eat around your menstrual cycle phases.

There’s a shift in energy metabolism over the month

Over the course of your cycle, your body changes the way it uses stored energy.

During the early and follicular phase, your body is much more dependant on carbs as a primary fuel source, even at rest.

During the luteal phase though your body prefers to use fat as its primary substrate. 

A number of studies have found that during this phase, fat oxidation is increased (particularly during rest, light activity, and moderate intensity exercise) whereas during the follicular phase it is lower [7]. 

Elevated estrogen (and estradiol) as well as progesterone levels are more than likely contributing factors for the shift in fat oxidation and enhanced fat use during exercise [8].

Insulin sensitivity and cravings

During your follicular phase your insulin sensitivity is relatively high. This means that higher carb meals and refeeds will compliment the intense, glycogen-depleting workouts you’re putting yourself through in the gym.

Because your insulin sensitivity is much lower in the luteal phase (and consequently your blood sugar is less stable), you’ll probably begin to get cravings for sugary or high-fat foods – basically anything with a high energy density. 

You may at this stage already be suffering low mood, and a sugar hit helps to release the mood-regulating neurotransmitter serotonin so the cravings could be pretty strong.

It is important to do all you can to fight these cravings, but a flexible diet that allows some high-calorie foods whilst still maintaining a deficit is more appropriate here than a strict restrictive dietary approach.

Water retention

Many women complain about water retention throughout their cycle. And although it affects each woman differently, fluid retention commonly occurs when progesterone is high – in the luteal phase. 

This will more than likely make you heavier on the scales due to excess water weight.

Pre-menstrual syndrome (PMS), which is characterised by irritability, emotional tension and water retention, are common symptoms right before your period (4-7 days beforehand for most women). Fluid retention can also occur pre-ovulation too in some women.

Excess water weight is another reason why higher-intensity exercise might be best avoided during the luteal phase – just down to it being uncomfortable more than any physiological mechanism as such.

Once your period starts and your body temperature returns to normal your water retention will begin to disappear and your body mass will regulate.

When to weigh yourself

Although scale weight isn’t the whole story of fat loss, it may still be important to chart progress, particularly in those who are overweight and wish to achieve a healthy body mass.

It goes without saying that weight loss and weight gain won’t be linear over the duration of your cycle. Water weight alone can fluctuate massively and send the dial on the scales spinning in all directions.

It is recommended that a seven-day rolling average of your weight is taken to chart progress, rather than a week-by-week differences. This takes into account water retention and hormonal changes that can compound changes to body fat and muscle mass.

It is also useful to compare measurements from one phase to the next, for example looking at body weight in early follicular phase one month, then looking at differences in the same phase the following month.

HOW DO YOU CYCLE NUTRIENTS TO MAXIMISE FAT LOSS?

During the follicular phase you’ll find that upping your carb intake helps to get you through the more intense workouts you’ll be putting into your programme. Your insulin sensitivity is high and your blood glucose is more stable.

During the luteal phase you’ll want to focus on keeping your cravings and carb intake under control with insulin sensitivity being low. 

A relatively reduced carb intake with higher fats works well. And the fact that your energy expenditure and metabolic rate increase slightly during this phase means that the additional calories from fats isn’t an issue for maintaining an energy deficit.

Current research on nutrient periodisation

There’s a fair bit of research to back up cycling nutrients around your menstrual cycle. This is sometimes referred to as a ‘menstralean diet’.

One recent study, published in the American Journal of Clinical Nutrition, found that when a group of healthy but overweight women followed a six-month weight loss programme adapted to metabolic changes over the menstrual cycle, they lost a significant amount of weight in comparison to the control group, who followed a basic calorie deficit [9].

They added more carbs in the follicular phase (and reduced fats), and then added more calories from fats (avocado and olive oils for example) whilst reducing carbs during their luteal phase, and added foods to help reduce cravings such as dark chocolate due to its high magnesium content.

The authors suggested that “a differentiated diet and exercise program that is tailored to counteract food cravings and metabolic changes throughout the menstrual cycle may increase weight loss above that achieved with a traditional diet and exercise program”.

Are there any supplements you should consider?

It is important that you prioritise getting all of your nutrients from food sources before considering adding in supplementation.

That said, there are a small number of supplementary nutrients that you can cycle into your menstralean diet to optimise fat loss.

A general multivitamin taken with food would be a good starting point, especially in a calorie deficit. Other than that, the following may be beneficial if you feel you might be deficient in specific nutrients:

• Vitamin D3 – important for bone and cardiovascular health. Recommended doses for trained athletes are variable, but 2000-4000 IU per day seems most appropriate.
• Iron – common nutrient deficiency leading to reduced performance, thyroid function and anemia.
• Calcium – important to promote fat loss and bone health. Splitting doses of ~1200 mg total per day seems to work well.
• Magnesium – 400 mg of magnesium citrate may help to alleviate symptoms of PMS and improve sleep

In order to maximize absorption, aim to take each supplement with foods containing that nutrient. 

For example, calcium supplements should be taken with dairy foods, and vitamin D could be taken with fatty fish.

Menstrual disruptions – not all clients are the same

So at this stage, you’ll be hopefully ready to apply what you’ve learned to your programmes. And rightly so. 

But before you do though, bear this in mind…. not all cycles are ‘normal’ and therefore not all of the above advice suits every woman.

As well as person-by-person variance on the timings of each phase, you may also experience menstrual disturbances – times when your period becomes irregular or even stops.

Firstly, oral birth control pills cause menstrual disturbance, as they block ovulation by inhibiting the LH surge we talked about in the follicular phase. Remember, it is LH that acts as a pin to puncture the follicle and release the egg. This, in turn, blocks menstruation.

Common non-medicine related disturbances include luteal phase defect (where progesterone levels are too low), anovulation (ovulation does not occur), oligomenorrhea (infrequent periods). In the case of each of these, advice needs to be given to the individual and their specific symptoms.

But the most important disturbance is that of amenorrhea.

What is Amenorrhea?

Amenorrhea is the absence or cessation of your period. It is a very complicated hormonal disorder with a number of possible root causes.

It is important that you are aware of this disorder as those that workout regularly and intensely are at a much higher risk of their period stopping than non-trained women.

What are the causes of amenorrhea?

Primary amenorrhea refers to the absence of menarche – the first menstrual cycle. This means that periods don’t start by 16 years old, but normal maturation has developed.

Secondary amenorrhea refers to any female that has experienced menarche but bleeding stops for three or more consecutive cycles.

Who is at risk?

Firstly, those that regularly participate in sports or exercise frequently are at a much higher risk of amenorrhea. Current statistics suggest that 69% of women athletes will experience a loss of cycle due to secondary amenorrhea at some point [10]. This is in comparison to less than 5% for untrained women.

Those that participate in sports that have an emphasis on low body mass such as physique, ballet, gymnastics and diving show highest incidences of all.

Why would you lose your period?

Rapid decreases in body mass and/or body fat seem to be the trigger for a loss of menstrual cycle. A low body mass index, in particular, seems to be a big risk factor.

And low body weight is typically caused by low energy availability – a calorie deficit that is too aggressive, causing a reduction in both fat and fat-free mass. There is also a strong link between disordered eating patterns/clinical eating disorders and amenorrhea as well.

When low body mass occurs, your hypothalamus doesn’t trigger the pituitary gland to release LH. And as we know by now, if there’s no trigger from LH there’s no ovulation. This is what’s referred to as functional hypothalamic amenorrhea.

Does dieting affect your period?

Yes. If you achieve a rapid or aggressive calorie deficit and weight loss, you’ll soon inhibit the hypothalamic-initiated release of LH. That, in turn, will reduce ovulation and your period can stop.

It is therefore important to either hit an aggressive calorie deficit for shorter periods of time, or to cruise in more gradually while still being able to train hard in the gym.

Should you be concerned if your period stops?

No. At least not in the short term.

Women aren’t meant to be hitting mega low body fat numbers. But to be successful in aesthetic sports you have to, and this can increase your risk of intermittent amenorrhea.

However, once competition has finished, it is recommended that you focus on rectifying the triggers that caused your period to start and focus on achieving a healthy body mass and body composition. This can be physical in terms of increasing your body weight; and psychological in terms of your attitude towards an increase in calorie intake.

Reversing menstrual cycle dysfunction

Your priority when wanting to kickstart your cycle is to increase energy availability. Because low energy availability was more than likely the cause of secondary amenorrhea, focusing on upping your calories is a priority.

You can also combine this with a reduction in physical activity and energy expenditure. If you do this correctly, your body weight and fat mass will begin to increase.

You should do this for an initial period of 2-4 weeks, or 6-8 weeks if you are an inexperienced athlete. Calories can be adjusted to suit, but a moderate calorie surplus works well.

Studies show that reducing training by just one session per week, coupled with an increase in calories by 200-350 can also have a kickstart effect on periods.

There is no real way of predicting how soon your cycle will begin, but studies show good success rates within 2-6 months [11]. There also appears to be a ‘set point’ weight gain of 2kg (4.5lb) that triggers ovulation.

A Final Point

For some trainers, there might be the initial fear or trepidation about asking questions about menstrual cycles to female clients. Blatantly asking a client outright where they are on their cycle might at this point feel like a bridge too far – but it should really be as easy to ask as “how are you feeling today?” or “did you get a good night’s sleep?”

To be the best trainer that you can be you need to consider the importance of monthly cycles on everything from energy and mood to nutrient partitioning. Planning it into the way you deliver programs will only make you a better trainer.

References

1. Davidsen, L et al. Impact of the menstrual cycle on determinants of energy balance: a putative role in weight loss attempts. Int J Obesity. 2007; 12: 1777-85
2. Nagashima, K et al. Thermoregulation, and menstrual cycle. Temperature. 2015; 2(3): 320-321
3. Garcia, AMC et al. Luteal phase of the menstrual cycle increases sweating rate during exercise. Braz J Med Biol Res. 2006; 39(9): 1255-1261
4. Janse de Jonge, XA. Effects of the menstrual cycle on exercise performance. Sports Med. 2003; 33: 833-851
5. Solomon, SJ et al. Menstrual cycle and basal metabolic rate in women. Am J Clin Nutr. 36(4): 611-6
6. Sung, E et al. Effects of follicular versus luteal phase-based strength training in young women. Springerplus. 2014; 3: 668
7. Zderic, TW et al. Glucose kinetics and substrate oxidation during exercise in the follicular and luteal phases. J Appl Physiol. 2001; 90: 447-453
8. Ashley, CD et al. Menstrual phase effects on fat and carbohydrate oxidation during prolonged exercise in active females. JEP. 2000; 3(4): 67-73
9. Geiker, N et al. A weight-loss program adapted to the menstrual cycle increases weight loss in healthy, overweight, premenopausal women: a 6-mo randomized controlled trial. Am J Clin Nutr. 2017; 105(6)
10. Abraham, SF et al. Body weight, exercise and menstrual status among ballet dancers in training. Br J Obstet Gynaecol. 1982; 89(7): 507-10
11. Cialdella-Kam, L et al. Dietary intervention restored menses in female with exercise-associated menstrual dysfunction with limited impact on bone and muscle health. Nutrients. 2014; 6(8): 3018-39